1. Technical Field
Embodiments of the invention disclosed herein relate generally to compositions and methods for altering hepatocyte growth factor activity or c-Met receptor activity. Certain aspects relate to the diagnosis, prevention or treatment of, as well as to general therapy of subjects having, suspected of having, or susceptible to, a condition associated with c-Met receptor dysregulation. C-Met receptor dysregulation may be a condition in which underactivity, overactivity or improper activity of a c-Met cellular or molecular event is present, including a hyperproliferative disorder, a condition characterized by abnormal angiogenesis, or alternatively, a condition characterized by vascular insufficiency such as may benefit from increased angiogenesis. Embodiments disclosed herein further relate to methods for identifying or modifying compounds useful for the diagnosis, prevention or treatment of such conditions associated with c-Met receptor dysregulation.
2. Description of the Related Art
The classic rennin-angiotensin system regulates cardiovascular function including blood pressure, electrolyte balance, reproduction, and may play a role in other physiological processes, including atherosclerosis. These angiotensin-mediated effects are believed primarily to operate through angiotensin (AT) receptors identified as AT1 and AT2 receptors. Renin, through its proteolytic activity, first cleaves the angiotensinogen precursor polypeptide to form angiotensin I. Next, angiotensin converting enzyme (ACE) enzymatically converts angiotensin I to angiotensin II; ACE has been detected in a variety of tissues including brain, kidney, adrenal glands, vasculature, heart and ovaries. ACE-generated angiotensin II (AT2 or AT2) is subsequently cleaved (by aminopeptidase A) to form angiotensin III, which is cleaved by aminopeptidases N, M and/or B to form angiotensin IV (Val-Tyr-Ile-His-Pro-Phe, [SEQ ID NO:33]). (Mustafa et al., J. Renin Angiotens. Aldoster. Syst. 2(4):205-210, (2001), Thomas et al., Int. J. Biochem. & Cell Biol. 35: 774-779 (2003); McKinley et al., Int. J. Biochem. & Cell Biol. 35: 901-918 (2003).)
Angiotensin IV (AT4 or AT4) has been shown to play a role in regulating disparate biological activities including blood flow, cognitive function, neuronal development, inflammation and behavior (Wright et al., Prog. Neurobiol. 72: 263-293 (2004); Kamar et al., Regul. Pept. 68: 131-138 (1997).) AT4 is believed to exert its biological effects through interaction with a cell surface receptor identified as the AT4 receptor (AT(4)R), which is also known as the insulin-regulated membrane aminopeptidase (IRAP) (e.g., Chai et al., 2004 Cell. Mol. Life. Sci. 61:2728; Esteban et al., 2005 Circ. Res. 96:965; Albiston et al., 2001 J. Biol. Chem. 276:48623). AT(4)R/IRAP is a type II (see, e.g., Parks, 1996 J. Biol. Chem. 271:7187) integral membrane-spanning protein having aminopeptidase activity.
Many of the observed biological characteristics of the AT4 system (e.g., the existence of both agonist and antagonist AT4 ligands), however, have been difficult to reconcile with the IRAP model for the AT4 receptor. This discrepancy suggested that another unidentified protein(s) might be responsible for the action of AT4 receptor ligands (Harding et al., 1994 Kidney Int. 46:1510; Wright et al., 2004 Prog. Neurobiol. 72:263). The molecular identity of the target AT4 receptor that mediates a number of AT4 biological activities has, however, remained elusive.
Hepatocyte growth factor (HGF, e.g., 1991 Proc. Nat. Acad. Sci. USA 88:7001; GenBank Accession No. AAA64239 [SEQ ID NO:83], M73239.1 (728 amino acids)), also known as scatter factor (SF), is a growth factor that induces cell motility and cell proliferation, which may lead to normal processes of angiogenesis, or abnormal processes of tumor development or metastasis. HGF functions by binding to its cell surface receptor, c-Met, which is a receptor protein tyrosine kinase and a protooncogene product.
The c-Met receptor is a heterodimer composed of an alpha and beta chain (Maggiora et al., J. Cell Physiol. 173:183-186, (1997), Christensen et al., Can. Lett. 225: 1-26, (2005)). The c-Met receptor is enriched on vascular endothelial cells where it mediates the regulation of angiogenesis (Rosen et al., 1997 EXS 79:193). For instance, NK4, a large molecule c-Met inhibitor, has been shown previously to inhibit angiogenesis (Kuba et al., 2000 Cancer Res. 60:6737).
Upon activation, as may result from ligand engagement, the c-Met polypeptide (e.g., hepatocyte growth factor-receptor, HGF-R, also known as scatter factor receptor, SF-R, GenBank Acc. No. AAA59591, [SEQ ID NO:84]) induces mitogenic, motogenic and morphogenic responses by recruiting a number of signaling and docking molecules, and has been implicated in the phosphorylation of cell junction proteins (e.g., Zhang et al., 2003 J. Cell Biochem. 88:408; Miao et al., 2003 J. Cell Biol. 162:1281; Berdichevsky et al., 1994 J. Cell Sci. 107:3557). Ligand induced activation of c-Met by HGF/SF leads to the autophosphorylation of specific tyrosine residues within the c-Met receptor protein tyrosine kinase (PTK) domain (Furge et al. (2000) Oncogene 19, 5582-5589; Weidner et al. (1995) Proc Natl Acad Sci USA 92, 2597-2601) and to the association of various signaling proteins (e.g., Naldini et al., 1991 Mol. Cell. Biol. 1250:1085). A significant event in c-Met signaling is the association with the c-met receptor of growth factor receptor bound protein 2, Grb2 associated binder (Gab1), a multi-functional scaffolding adapter (Birchmeier et al., 2003 Nat. Rev. Mol. Cell. Biol. 4:915). Gab1 association provides c-Met with multiple docking sites for a variety of intracellular signal transducers (Trusolino et al., 2002 Nat. Rev. Cancer 2:289).
Following activation by HGF/SF, c-Met is able to exert a variety of effects by recruiting docking and signaling molecules. Phosphorylation of the tyrosine residues in the activation loop of the PTK domain potentiates the intrinsic kinase activity of Met, whereas phosphorylation of the two docking site tyrosine residues (Tyr1349, Tyr1356) allows for the recruitment of adaptor molecules including Grb2, SHC and Gab 1 and signaling enzymes including phosphotidylinositol 3-kinase (PI3K), phospholipase Cγ (PLC-γ), the PTK src, the protein tyrosine phosphatase SHP2, as well as the transcription factor STAT3 (reviewed in Furge et al. (2000) Oncogene 19, 5582-5589).
The binding of HGF to the cell surface c-Met receptor thus results in multiple cell-signaling events that promote cell survival, cell proliferation, cell motility, disruption of the extracellular matrix (ECM), cell morphogenesis, angiogenesis and/or cell extravasation and colonization, for instance, as observed in tumor metastasis. (Jeffers et al., J. Mol. Med., 74: 505-513 (1996); Amicone et al., EMBO J. 16: 495-503 (1997); Matsumoto and Nakamura, Biochem. Biophys. Res. Comm. 239: 639-644 (1997); Kirchhofer et al., J. Biol. Chem., 279: 39915-39924 (2004)). Disruption of normal signaling through c-Met has been implicated in certain cancers (e.g., Zhang et al., 2004 Cancer Cell 6:5; Christensen et al., 2005 Cancer Lett. 225:1-26; Ferraro et al., 2006 Oncogene 25:3689). For example, overexpression of HGF and/or of c-Met has been implicated in a number of cancers, including carcinomas, gliomas, and mesotheliomas. Particular organs affected include breast, pancreas, liver, lung, ovary, stomach, bile duct, kidney, and others, in part because of increased angiogenesis (Zbar et al., J. Urol., 151: 561-566 (1994); Date et al., FEBS Letters, 420:1-6 (1997)). In addition, several studies have indicated that cancer cells can be a significant source of HGF within a subject (e.g., Jiang et al., Onc. Hemat. 53: 35-69 (2005)).
Alterations (e.g., statistically significant increases or decreases) in the activity states of a number of intracellular signaling cascades thus characterize cellular responses to HGF binding by the cell surface c-Met receptor, including biological signal transduction pathways that comprise one or more of Grb2, cortactin, Arp2/3, WASP/Wave, Rho/rac, Rock, LIMK, PI1P5-K, ERM proteins, Dia-1, MLC phosphatase, cofilin, Ptdins(4,5)P2, cadherins (including E-cadherin), MMPs, fl-catenin, p27kip1, SOS, Ras, Raf, MAPK, PI3K, NK B, src, JNK1, Bid/Bax, caspases, C-Myc, Bax, Mcl1, Bcl-w, Akt, FLICE, STATs (including STAT3), COX, ERK/paxillin, as well as others (see, e.g., Jiang et al., Onc. Hemat. 53: 35-69 (2005); Alberts et al., Molecular Biology of the Cell, 4th Ed., 2002, Garland Science, NY). Activation of these intracellular messenger systems can lead to changes in a cell's cytoskeleton, adhesion state and adherens junctions, cell cycle, and directional cell movement, and may also contribute to altered activity in one or more of a number of other biochemical pathways that affect cellular metabolic, catabolic, biosynthetic, respiratory, gene expression, membrane dynamic or other functions or phenotypes. Thus, such HGF-c-Met binding events may lead to or contribute to cancer development, tumor cell growth or metastasis, altered angiogenesis, or other physiologically significant outcomes.
Angiogenesis, the process of blood vessel formation, is necessary for proper wound healing and repair, as well as playing an important role during embryonic, fetal and young animal development, and continuing on to adulthood. Dysfunction in the course of angiogenic processes at any of these stages may result in certain detrimental health conditions, including, for instance, ischemic heart disease, preeclampsia, neurodegeneration, and/or respiratory distress (e.g., as the result of an inadequate or insufficient level of angiogenesis relative to the levels seen in unafflicted individuals), and also including, for example, malignant metastasis, arthritis, macular degeneration, diabetic retinopathy, ocular and inflammatory disorders, obesity, asthma, diabetes, cirrhosis, multiple sclerosis, endometriosis, AIDS, bacterial infections, and/or autoimmune diseases (e.g., as the result of an excessive or overabundant level of angiogenesis relative to the levels seen in unafflicted individuals). See, e.g., Carmeliet, Nature 438:932-936 (2005). Intervention to alter (e.g., increase or decrease in a statistically significant manner) angiogenesis in these and other conditions remains a useful but incompletely fulfilled goal.
Clearly there is a need for improved compositions and methods to regulate cellular processes such as cell proliferation, cell motility and cell survival, that have clinical relevance to cancer, inflammatory disease, and other conditions. By advancing the understanding of biological signal transduction mechanisms that operate through the c-Met receptor, the present invention provides such compositions and methods and offers other related advantages.